Most computer application programs dating back more than about a decade use a text-based user interface, in which the user types commands on a keyboard, and output from the application is displayed on a text screen. With the advent of computer interface technology that supports the displays of graphical images, Graphical User Interfaces (GUI's) have become popular. A GUI application can be controlled through menu bars, buttons, sliders, or similar control elements drawn by the application on the display screen. The user interacts with a GUI application using a pointing device, such as a mouse, to move a cursor across the display and clicking a mouse button while pointing at a menu or one of the other graphical controls provided by the application.
Window systems allow multiple applications to run side-by-side on the same display by dividing the screen into separate, possibly overlapping, rectangular areas (windows). Window systems typically support GUI applications as well as older, text-based applications running in a window that emulates a character terminal. Examples of such window systems are the Apple Macintosh operating system, the X-Window system under the Unix operating system, Microsoft Windows running under DOS, and the IBM OS/2 Presentation Manager.
Integrated Graphical User Environments go one step further by supporting a graphical mode of interaction between different applications running in different windows. Examples of such environments are integrated application packages, e.g., Computer Aided Software Engineering (CASE) systems, as well as so-called Object Oriented User Interfaces (OOUI's). In a OOUI environment the user interacts with the system by manipulating iconic representations of system resources (data files, application programs, printers or other I/O devices, etc) on the screen. For example, to print a document, the user moves the cursor to the icon representing the file containing the document, presses down a mouse button, moves the cursor to an icon representing a printer, and releases the mouse button. For another example, a user might initiate a text editing operation on a pre-existing text file by using the mouse as above to select a text file icon in a directory browser window, move the icon to a window in which a text editor is running, and release the text file icon onto the window. This type of interaction is called "drag and drop", because an object selected in one window is "dragged" to another window where it is "dropped". Examples of OO GUI environments are the IBM OS/2 2.0 Work Place Shell, as well as so called "desktop managers" available for DOS (Norton Desktop) and Unix (Xdt, HP-VUE, OpenLook, etc).
A drawback of these environments is that applications integrated in the environment must follow a specific protocol to interact with the other applications. Typically, communicating among application programs in a graphical user interface environment requires all programs to follow a pre-established protocol, such as the communications conventions of the Andrew Toolkit. Existing applications cannot be integrated into the environment without re-engineering and rewriting the application. Processes which do not follow the protocol, i.e., are not implemented with the specific interfaces, are left non-integrated. For instance, in the text editing example discussed above, if the directory browser program and the text editor program are not part of the same integrated package, then the directory browser will not know how to communicate that the user desires to edit a selected file to the text editor. Thus, the directory browser will not be able to initiate the desired operation by the text editor.
Therefore, how to integrate existing and new applications without requiring such imbedded interfaces has been a continuing problem, and users have had limited ability to integrate the different applications which their systems support.
U.S. Pat. No. 5,075,847, issued to Fromme and titled "Method and Apparatus for Computer Program Encapsulation", describes a method for integrating a text-based application tool into a CASE system without modifying the application code. An interface description file specifies the layout of a graphical user interface for the application tool as well as the desired operations in response to interactions with the user interface and with other tools. However, the Fromme method is restricted to text-based applications only. As described in column 8, lines 49-53,
The application tools selected for encapsulation in accordance with the present invention must conform to the UNIX pipe model of communication. Communication with the application tool is in the form of character string inputs and character string outputs.
In the Fromme system, the user interface for the application, as specified in the interface description file, is created and controlled by the CASE system. The system uses the Unix pipe facility to control the application by sending commands as character strings to the standard-input stream (stdin) of the application and intercepting its standard-output stream (stdout) to display the output in a window created by the CASE system. Therefore, the Fromme method is unsuitable for integrating GUI applications into a graphical user environment, because such applications do not follow the UNIX pipe model. Rather, such GUI applications create their own user interface and cannot be controlled through stdin and stdout.